The Nitrogen Cycle and Human Impacts

Vocabulary flashcards covering the processes, reservoirs, chemical transformations, and human impacts associated with the nitrogen cycle.

Nitrogen Cycle

The movement of nitrogen molecules between sources, sinks, and reservoirs.

Nitrogen Reservoirs

Locations such as plants, soil, and the atmosphere that hold nitrogen, generally for a relatively short period of time when compared with carbon cycle reservoirs.

Atmosphere (Nitrogen Cycle)

The largest reservoir of nitrogen, containing about $78\%$ nitrogen, mostly existing in the form of unusable $N_2$ gas.

Nitrogen Fixation

The first and most critical step in the nitrogen cycle for life on Earth, converting atmospheric $N_2$ gas into biologically usable forms like ammonia ($NH_3$) or nitrate ($NO_3$).

Legumes

Plant species such as peas and beans that have root nodules containing symbiotic nitrogen-fixing bacteria.

Synthetic Nitrogen Fixation

An industrial process where humans combust fossil fuels to fix atmospheric nitrogen gas into nitrates ($NO_3$) to produce synthetic agricultural fertilizers.

Assimilation

The process where plants take in nitrates or ammonia through their roots and animals eat plants or other animals to incorporate nitrogen into their DNA and proteins.

Ammonification

The process where soil bacteria, microbes, and decomposers break down biological waste and dead organic matter, returning nitrogen to the soil as ammonia.

Nitrification

The process conducted by soil bacteria where ammonium ($NH_4$) is converted into nitrite ($NO_2$) and eventually into nitrate ($NO_3$).

Denitrification

The process where soil bacteria convert soil nitrogen, specifically nitrate, back into a gas form known as nitrous oxide ($N_2O$).

Nitrous Oxide ($N_2O$)

A greenhouse gas produced by soil bacteria during denitrification, particularly in waterlogged or over-irrigated agricultural soils, that traps heat in Earth's atmosphere.

Ammonia Volatilization

The release of ammonia gas into the atmosphere from excess fertilizer, which can cause acid precipitation, irritate human respiratory tracts, and lead to lost farmer profits.

Leaching

The process where rainwater or irrigation water carries over-applied nitrates right out of agricultural soil and into local bodies of water.

Eutrophication

An environmental issue where excess nitrogen in bodies of water fuels aggressive surface algae growth, blocking sunlight and killing aquatic plants below the surface.